Reorganization of spinal circuitry and removal of supraspinal influences after spinal cord injury (SCI) result in pathophysiologic conditions, such as motor and autonomic hyperflexia (AH) in response to noxious stimuli. Individuals with SCI are thus at increased risk during surgical procedures and require special anesthetic management, but few studies that have addressed this problem. An animal model to assess changes in anesthetic effects on spinal reflexes following SCI would aid in developing effective anesthetic management of the SCI population. Changes in anesthetic (isoflurane) effects on motor and sympathetic reflex pathways after acute and chronic spinalization, and the effects of NMDA antagonists on these changes, will be investigated in rats. These will be studied using quantitative measurement of responses evoked by noxious stimuli (pinch, heat), including limb movement, blood pressure, and electrophysiological recording of single dorsal horn neurons, along with simultaneous recording of sympathetic and motor nerve activity. Changes in isoflurane dose-response functions for these parameters., and correlations among them, will be determined before and after acute (complete and partial) and chronic spinalization. Thus, these studies aim to determine how and where changes in spinal reflex pathways occur after SCI, and how they relate to anesthetic requirements. This knowledge will lead to safer anesthesia in SCI patients, and to a better understanding of nociceptive/spinal reflex pathways occur after SCI, and how they relate to anesthetic requirements. This knowledge will lead to safer anesthesia in SCI patients, and to a better understanding of nociceptive/spinal reflex pathways, their supraspinal control, and changes in spinal circuitry following SCI.